This invention relates to the desulfurization of hydrocarbon feedstocks, and most particularly to the desulfurization of reformer feedstocks by contact with a catalytic absorbent.
Petroleum refining processes such as catalytic reforming are utilized for such purposes as hydrogenation and dehydrogenation, cyclization and dehydrocyclization, and isomerization and dehydroisomerization of selected hydrocarbons. Catalytic reforming processes play an integral role in upgrading straight run or cracked naphtha feedstocks, as by increasing the octane number of the gasoline fraction contained in such feedstocks. In a typical reforming process treating a straight run naphtha or cracked naphtha, the feedstock is upgraded by contact with a catalyst comprising a noble metal on alumina. Conditions utilized in reforming processes vary depending upon such factors as the type of feed processed and the desired increase in octane level.
To achieve maximum run lengths and increase process efficiency, it is generally recognized that the sulfur content of the feedstock must be minimized. Reforming catalysts, and particularly those comprising platinum, and most particularly comprising platinum and rhenium, deactivate rapidly in the presence of sulfur compounds, and as a result, it is necessary to reduce the sulfur content of reformer feedstocks as low as possible. Preferably, feedstocks contacted with reforming catalysts are desulfurized to contain less than 0.1 ppm by weight sulfur.
A common method of treating reformer feeds to reduce the sulfur content is by hydrodesulfurization wherein a naphtha or other feedstock is contacted with a sulfur-tolerant hydrogenation catalyst in the presence of hydrogen. The sulfur in the feedstock is converted by hydrogenation and cracking to hydrogen sulfide, which may be separated from the naphtha by conventional means prior to reforming. Although good sulfur removal may be achieved by hydrodesulfurization units operating under severe conditions, the efficiency of such processes is ultimately limited by equilibrium and/or kinetic considerations. In many instances, it is not possible to obtain hydrodesulfurized products containing less than 0.1 ppmw sulfur as desired in most reforming operations. Furthermore, it is impossible to guard against upsets in the hydrodesulfurization unit which can result in high levels of organo-sulfur compounds remaining in the reformer feedstock.
In addition to hydrodesulfurization, there are other methods employing catalytically active materials for removing sulfur from hydrocarbons. Such methods reduce the sulfur content of the hydrocarbon by "absorbing" sulfur therefrom and generally employ a catalytically active absorbent material under nonhydrogenative conditions. Usually, the absorbent material contains a metal component, such as nickel, copper, or silver, and the feedstocks generally treated are reformer feedstocks, particularly naphthas. Typical of such processes include that disclosed in U.S. Pat. No. 2,767,759 to Annable wherein a bed of nickel molybdate pellets is utilized to reduce the sulfur content of naphthas. Similarly, in U.S. Pat. No. 4,704,947 to Jacobson et al., the use of copper components supported on conventional carriers is disclosed for reducing the thiol content of naphthas by absorption. In addition, Thorn in U.S. Pat. No. 2,876,196 describes a method for desulfurizing hydrocarbon feedstocks by contact with catalytic particles comprising platinum supported on a suitable carrier, and sulfur-contaminated aromatic hydrocarbons have been purified with supported nickel components under non-hydrogenative conditions as taught by Davis in U.S. Pat. No. 3,485,884.
One object of the present invention is to provide an improved process for removing sulfur from naphthas and other feedstocks under non-hydrogenative conditions with a catalytic material useful for absorbing sulfur compounds from the feed. A specific object is to provide a process useful for lowering the sulfur content of reformer feeds to below 0.1 ppm by weight. A further object is to enhance the sulfur absorption capacity of nickel-containing absorbents by the addition of platinum group metal promoters. Other objects and advantages will be more apparent in view of the following detailed description.